Britain’s tax authorities have given Goldman Sachs an unusual and generous Christmas present, leaked documents reveal. In a secret London meeting last December with the head of Revenue, the wealthy Wall Street banking firm was forgiven £10m interest on a failed tax avoidance scheme.

HM Revenue and Customs sources admit privately that the interest-free deal is “a cock-up” by officials, but refuse to say who was responsible.

Documents leaked to Private Eye magazine and published in full by the Guardian record that Britain’s top tax official, HMRC’s permanent secretary Dave Hartnett, personally shook hands on a secret settlement last December.

Hartnett is due to be questioned on Wednesday by the Commons public accounts committee. The leaked documents suggest that a previous PAC chairman, Edward Leigh, was misled when he was told it was illegal to reveal details of such cases to parliament.